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A pRNA-induced structural rearrangement triggers 6S-1 RNA release from RNA polymerase in Bacillus subtilis.

ABSTRACT: Bacillus subtilis 6S-1 RNA binds to the housekeeping RNA polymerase (?(A)-RNAP) and directs transcription of short 'product' RNAs (pRNAs). Here, we demonstrate that once newly synthesized pRNAs form a sufficiently stable duplex with 6S-1 RNA, a structural rearrangement is induced in cis, which involves base-pairing between sequences in the 5'-portion of the central bulge and nucleotides that become available as a result of pRNA invasion. The rearrangement decreases 6S-1 RNA affinity for ?(A)-RNAP. Among the pRNA length variants synthesized by ?(A)-RNAP (up to ?14 nt), only the longer ones, such as 12-14-mers, form a duplex with 6S-1 RNA that is sufficiently long-lived to induce the rearrangement. Yet, an LNA (locked nucleic acid) 8-mer can induce the same rearrangement due to conferring increased duplex stability. We propose that an interplay of rate constants for polymerization (k(pol)), for pRNA:6S-1 RNA hybrid duplex dissociation (k(off)) and for the rearrangement (k(conf)) determines whether pRNAs dissociate or rearrange 6S-1 structure to trigger 6S-1 RNA release from ?(A)-RNAP. A bioinformatic screen suggests that essentially all bacterial 6S RNAs have the potential to undergo a pRNA-induced structural rearrangement.

SUBMITTER: Beckmann BM

PROVIDER: S-EPMC3321203 | biostudies-literature | 2012 Apr

REPOSITORIES: biostudies-literature

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A pRNA-induced structural rearrangement triggers 6S-1 RNA release from RNA polymerase in Bacillus subtilis.

Beckmann Benedikt M BM Hoch Philipp G PG Marz Manja M Willkomm Dagmar K DK Salas Margarita M Hartmann Roland K RK

The EMBO journal 20120214 7

Bacillus subtilis 6S-1 RNA binds to the housekeeping RNA polymerase (σ(A)-RNAP) and directs transcription of short 'product' RNAs (pRNAs). Here, we demonstrate that once newly synthesized pRNAs form a sufficiently stable duplex with 6S-1 RNA, a structural rearrangement is induced in cis, which involves base-pairing between sequences in the 5'-portion of the central bulge and nucleotides that become available as a result of pRNA invasion. The rearrangement decreases 6S-1 RNA affinity for σ(A)-RNA ...[more]

PMID: 22333917

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Project description:Here we investigated the refolding of Bacillus subtilis 6S-1 RNA and its release from σA-RNA polymerase (σA-RNAP) in vitro using truncated and mutated 6S-1 RNA variants. Truncated 6S-1 RNAs, only consisting of the central bubble (CB) flanked by two short helical arms, can still traverse the mechanistic 6S RNA cycle in vitro despite ~10-fold reduced σA-RNAP affinity. This indicates that the RNA's extended helical arms including the '-35'-like region are not required for basic 6S-1 RNA functionality. The role of the 'central bubble collapse helix' (CBCH) in pRNA-induced refolding and release of 6S-1 RNA from σA-RNAP was studied by stabilizing mutations. This also revealed base identities in the 5'-part of the CB (5'-CB), upstream of the pRNA transcription start site (nt 40), that impact ground state binding of 6S-1 RNA to σA-RNAP. Stabilization of the CBCH by the C44/45 double mutation shifted the pRNA length pattern to shorter pRNAs and, combined with a weakened P2 helix, resulted in more effective release from RNAP. We conclude that formation of the CBCH supports pRNA-induced 6S-1 RNA refolding and release. Our mutational analysis also unveiled that formation of a second short hairpin in the 3'-CB is detrimental to 6S-1 RNA release. Furthermore, an LNA mimic of a pRNA as short as 6 nt, when annealed to 6S-1 RNA, retarded the RNA's gel mobility and interfered with σA-RNAP binding. This effect incrementally increased with pLNA 7- and 8-mers, suggesting that restricted conformational flexibility introduced into the 5'-CB by base pairing with pRNAs prevents 6S-1 RNA from adopting an elongated shape. Accordingly, atomic force microscopy of free 6S-1 RNA versus 6S-1:pLNA 8- and 14-mer complexes revealed that 6S-1:pRNA hybrid structures, on average, adopt a more compact structure than 6S-1 RNA alone. Overall, our findings also illustrate that the wild-type 6S-1 RNA sequence and structure ensures an optimal balance of the different functional aspects involved in the mechanistic cycle of 6S-1 RNA.

Dataset Information

A pRNA-induced structural rearrangement triggers 6S-1 RNA release from RNA polymerase in Bacillus subtilis.

Publications

A pRNA-induced structural rearrangement triggers 6S-1 RNA release from RNA polymerase in Bacillus subtilis.

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